Non-transitory storage devices, including flash memories, Electrically Erasable Read-Only Memories (EEROMs), etc., are storage chips which won't lose data after they are powered off. In order to repeatedly utilize storage space of storage units in the non-transitory storage devices, data in the storage units is required to be erased in advance, and then, new data can be written into the storage units. A typical structure of storage units in a non-transitory storage device is configured as a matrix constituted of word lines along a row direction and bit lines along a column direction. When performing data erasing operations, by applying a data erasing voltage to the word lines, which is generally from 10V to 15V, data in the storage units corresponding to the word lines is erased.
When performing data erasing operations, in order to avoid breakdown of tunneling oxide layers of the storage units, it is required that the data erasing voltage applied on the word lines reaches around 12V after 200 μs. Accordingly, a climbing signal generation circuit is needed, so as to convert a high voltage erasing signal output from a charge pump into a voltage control signal with a relatively slow ascending speed.
In the climbing signal generation circuit, a startup voltage for a high voltage conduction tube coupled to the word lines becomes greater along with the increase of data erasing operations, leading to a drop of a maximum voltage output to the word lines, which affects the erasing effect. Conventionally, the erasing effect is improved by raising the voltage of the high voltage erasing signal. However, in this case, area of a high voltage generation unit generating the erasing signal is apparently enlarged, so that area occupied by the entire circuit is enlarged greatly.